Abstract: Described is a porous flexible sheet of about 93 to 99.5 weight percent amorphous precipitated silica and from about 0.5 to about 7 weight percent fibrillated, unsintered polymeric material, e.g., polytetrafluoroethylene. The sheet is useful as a separator in absorbed electrolyte gas recombinant batteries, e.g., lead-acid batteries, and has a tensile strength of less than 75 pounds per square inch (0.5 MPa). The sheet preferably has a porosity of from 85 to 92 percent and exhibits an electrical resistance of less than 3.5 milliohm-in.sup.2 /10 mil when saturated with 37 percent sulfuric acid. The sheet is prepared by subjecting a dry homogeneous mixture of the silica and polymeric material, e.g., polytetrafluoroethylene, in the above proportions to mechanical shear blending forces to fibrillate the polymer and thereafter dry forming the resulting admixture into sheet form.